1. Field of the Invention
The present invention is directed generally to an electrochemical gas sensor and, more particularly, to an electrochemical gas sensor with a compensated output.
2. Description of the Background
Electrochemical gas sensors are typically included in monitoring equipment to measure gas concentrations such as, for example, oxygen in a sample gas. The sensors typically display a numerical reading of the gas concentration and provide an output waveform corresponding to the gas concentration.
FIG. 5 illustrates a typical electrochemical gas sensor 10 of the relevant art. The sensor 10 includes a sensor body 12 which contains the components of the sensor 10. A cathode 14 can be constructed of, for example, a noble metal such as silver. An anode 16 can be constructed of, for example, lead. An electrolyte 18 such as, for example, an aqueous solution of potassium hydroxide, fills the sensor body 12. An expansion membrane 20 allows for expansion and contraction of the electrolyte 18 without damaging the sensor 10. A sensing membrane 22 contains the electrolyte 18 and limits the gas to be measured from having free access to the cathode 14, thus forming a diffusion barrier. The sensing membrane is constructed of, for example, Teflon.RTM., a product of DuPont.
The electrochemical processes governing most electrochemical sensors can respond to changes in gas concentrations rapidly at times on the order of milliseconds. However, many electrochemical sensors contain diffusion barriers such as the membrane 22. These sensors are unsuitable for monitoring rapid changes in gas concentrations because the diffusion barriers, dead volume, and other factors raise their response time to changes in gas concentrations to the order of seconds. The sensors generally suffer from predictable, repeatable, and gradual reduction in sensor output with an increase in the frequency of gas concentration fluctuations. Thus, there is a need for an electrochemical gas sensor which has a rapid output response time to rapid fluctuations in gas concentrations and that compensates for the natural degradation in frequency response.